Low-coordinate bis(imidazolin-2-iminato) dysprosium(iii) single-molecule magnets

Lanthanide-based single-molecule magnets (Ln-SMMs) have become the most conspicuous SMMs exhibiting the highest effective barrier (U-eff) and blocking temperature (T-B). Different strategies have been proposed to construct high-performance SMMs, including reducing the coordination number to generate high-order local symmetry and weakened molecular vibrations, thus reducing the possibility of spin-vibration interaction. However, the synthesis of low-coordinate Ln(iii) complexes is still very challenging owing to their large ionic radius and ionic nature, especially when the coordination number is lower than five. Herein, two bis(imidazolin-2-iminato) dysprosium(iii) SMMs [Dy(Im(Dipp)N)(2)(Bn)(THF)] (1) and [Dy(Im(Dipp)N)(2)(BPh4)] (2) (Im(Dipp)NH = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine, Bn = benzyl) were synthesized and characterized. The four-coordinate complex 1 possessed a U-eff of 593 K and a T-B of 8 K, while complex 2 exhibited a U-eff of 343 K. The weaker equatorial crystal field in 1 than 2 could suppress the quantum tunneling of magnetization (QTM), leading to a higher U-eff. Moreover, calculations on model structures indicated that constructing bis(imidazolin-2-iminato) single-molecule magnets with a higher U-eff and T-B is possible by further regulating the electronic effects and steric hindrance of imidazolin-2-iminato ligands.

Automated summary

Lanthanide-based single-molecule magnets (Ln-SMMs) have shown the highest effective barrier and blocking temperature among all SMMs. Different strategies, including reducing coordination number and weakening molecular vibrations, have been proposed to construct high-performance SMMs. However, the synthesis of low-coordinate Ln(iii) complexes remains challenging due to their large ionic radius and ionic nature.